Stationary sources of air pollution, e.g., electric power generating plants, produce exhaust gas streams that contain levels of NOx in excess of those permitted under Federal and State air quality regulations, even where the power plants utilize natural gas as the fuel (thereby avoiding emitting unburned hydrocarbons that would otherwise occur when the fuel consists of oil or coal). Typically, such plants reduce the NOx in the exhaust gas streams to N2 by injecting ammonia into the exhaust gas stream in the presence of a selective catalytic reduction (“SCR”) catalyst typically consisting of vanadia disposed on titania. Although the resultant gas stream contains levels of NOx below the maximum permitted under such regulations, the reaction that utilizes ammonia as the reducing agent also results in emissions of ammonia above that permitted under such regulations. Therefore, a further catalytic reaction is required wherein NH3 in the exhaust gas stream is selectively oxidized to N2 without the formation of amounts of NOx that would otherwise raise the level of NOx above that permitted by such regulations.
Typically, prior art ammonia oxidation catalysts not only cause the oxidation of NH3 to N2, but they also catalyze the oxidation of NH3 to NOx. Indeed, most prior art ammonia oxidation catalysts are designed to oxidize ammonia to nitrites and nitrates in order to produce useful quantities of nitric acid (HNO3). Typical prior art ammonia oxidation catalysts are described in the following exemplary U.S. Pat. Nos. 5,122,497; 5,336,656; 5,690,900; 6,165,435; 6,380,128; 6,489,264; and published U.S. patent application Ser. No. US2003/0124046.